mnesia:table_info(Tab, size) returning undefined

[lhoguin]

Describe the bug
Something unexpected happens to some RabbitMQ users: mnesia:table_info(Tab, size) returns undefined.

Related ticket in the Prometheus.erl project: deadtrickster/prometheus.erl#133

The related code is very simple: loop over all tables, get the size and sum the sizes up: https://github.com/deadtrickster/prometheus.erl/blob/master/src/collectors/mnesia/prometheus_mnesia_collector.erl#L196-L201

To Reproduce
Don't know!

Expected behavior
I am trying to figure out whether this is a real issue or whether we should handle undefined in the code. Modifying the code to handle undefined is simple enough but if this would hide a deeper issue I would like to figure that out if possible.

So should we expect mnesia:table_info(Tab, size) to return undefined?

Affected versions
24 at least based on reports.

[dgud]

When the table should be loaded on the local node but is not yet loaded it will return undefined.

[lhoguin]

Perfect, then we will just handle it in the code. Thanks!

[dgud]

I will NOT change this behavior since someone might have used that to check if a table is loaded.